1. Field of the Invention
The present invention relates to diode structures containing a-Si:H (amorphous silicon containing hydrogen) for use in image sensor arrays, wherein the a-Si:H arranged as a thin film between two conductive electrodes on a substrate of electrically insulating material.
2. Description of the Prior Art
The structure and manufacturing techniques for large-area inexpensive image sensors by means of thin film technology utilizing a layer of a Si:H disposed between two electrodes are discussed, for example, in a report by Holzenkaempfer et al. in the Proc. of the MRS Europe, Strasbourg (1984), at pages 575-579.
In addition to a high photo-sensitivity, sensors to be used, for example, in image sensor arrays, such as in office communications equipment, must also exhibit a low dark current, uniform current-voltage characteristics of the individual elements within an array, and a good stability even after being illuminated for a long time. Disparities and malfunctions in all of these areas can result from events occurring at the contact boundary surfaces of the sensors.
A highly blocking diode arrangement for use in sensor rows is described in an article by Kaneko et al in the Journal of Non-Crystalline Solids, 50/60 (1983) at pages 1227-1230. The diode arrangement described therein has a barrier layer of silicon nitride disposed between a transparent indium tin oxide electrode and a semiconductor body consisting of a-Si:H. The a-Si:H body consists of a double layer of intrinsic a-Si:H (2.5 nm) and p-type doped a-Si:H (200 nm). The barrier layer of silicon nitride is situated at the side of the semiconductor body (intrinsic a-Si:H) facing a glass substrate on which incoming light is incident. Manufacture of this known arrangement requires significant technological outlay because of the deposition of a plurality of layers, with the accompanying risk of doping entrainment in the deposition of the boron doped p.sup.+ intermediate layer of amorphous silicon.
Another structure for improving the blocking properties of sensor arrangements using a-Si:H as a photoconductor is described in a report by Yamamoto et al in the Extended Abstracts of the 15th Conference on Solid State Devices and Materials, Tokyo, 1983, pages 205-208. In addition to the photodiode, the diode arrangement described therein contains a blocking diode instead of a barrier layer. This structure requires a number of complex and time-consuming process steps to manufacture, because p.sup.+ and n.sup.n a-Si:H layers are used in addition to the a-Si:H layer, and these layers must be produced in different reactors. Moreover, as in the Kaneko arrangement, the risk of doping entrainment is also present.
Another blocking diode arrangement of this type is described in a report by Yamamoto et al in the Jap. J. Appl. Phys., 20 Suppl. 2, 185-188 (1981). The metals palladium and gold are used as electrodes.